This disclosure is generally directed to coated fertilizer particles including a fertilizer substance core coated with coating material that may comprise linear or branched aliphatic monocarboxylic acids. The coated fertilizer particles may also comprise sealants, such as waxes. Also disclosed is a method of making coated fertilizer particles.
In the agricultural industry, it is known to apply fertilizers in a granular or pastille form. Granulation has benefits both in storage and in dissemination of the fertilizer. Granulation can be achieved by various methods. For example, granular fertilizers can be produced through a chemical reaction where heat is generated to produce granulation of a liquid fertilizer (such as sulfuric acid, phosphoric acid, or ammonia) into a solid form. However, it is difficult to control the release characteristics of the fertilizer with granulation techniques.
Controlling the release rate of fertilizer to the soil has been recognized to be agronomically important. Such control can minimize loss of water-soluble fertilizers as a result of irrigation or heavy rainfall. Controlling the release rate of the fertilizer may also provide the following benefits: reducing the amount of applied fertilizer material that escapes into the aquasphere, which pollutes waterways; improving the uptake of fertilizer plant nutrient material by timing the release to match plants' needs; keeping the fertilizer nutrients in the root growing zone of the soil; and minimizing sequestration by adsorption at deeper levels where it is unavailable to the plant. In the case of plant micronutrients, controlled release of high analysis fertilizer material prevents the development of toxic concentrations of these materials, which are by definition required in very small quantities. Improving the spatial distribution of the micronutrient materials is also a benefit.
Sulfur has previously been used as a control release agent for fertilizers. Sulfur coated urea in various commercial forms is an example. However, there are problems associated with using only elemental sulfur for such purposes, such as difficulty controlling and varying the rate of release, or providing incomplete coverage or developing fractures with aging, which allows ingress of water and rapid depletion of the carried fertilizer material. Also, a process that depends solely on the degradation of sulfur by microbiological action to expose the carried fertilizer is hard to control and is markedly dependent on soil temperature. Formulations that perform well in tropical or subtropical climates may perform poorly in temperate or cool soils. Adjusting formulations and process conditions to meet these requirements using only elemental sulfur has not been well demonstrated.
Blending a swelling clay material with liquid elemental sulfur and solidifying to create a controlled release plant nutrient sulfate fertilizer is also known. The presence of the swelling clay in the solid sulfur particle accelerates the breakdown of the solid sulfur into a small particulate size distribution that promotes subsequent microbiological conversion of the sulfur to plant nutrient sulfate. Cheap and available elemental sulfur can thus be used to control the rate of release of sulfur into the soil.
Further attempts have been made to supplement sulfur as a control release agent by combining bentonite clays with sulfur to form a sulfur/clay matrix. An example of this composition is described in “Another Approach to S Forming,” Sulfur, September-October 1995 and in “Ground, Degradable Sulfur Granules Suitable for Bulk Blending,” Sulfur 99, 17-20 Oct. 1999. These articles describe sulfur granules produced in a granulation drum. The control of the granulation step is based on the recycle loop , which is fed continuously with ammonium sulfate seed crystals.
U.S. Pat. No. 6,749,659 discloses that a controlled release property can be imparted to a fertilizer formulation by combining the fertilizer material or materials with a coating, carrier matrix, or similar component comprising elemental sulfur in admixture with swelling clays.
Although the above attempts to control the release of a fertilizer substance into the soil have shown some success, the need still exists to provide a fertilizer composition that allows better controlled release of a fertilizer substance into the soil, and resists being washed away from plants by heavy rainfall or irrigation.
Although in a different field of endeavor, a few patents disclose coatings for controlling the release of nutrients in animal feeds, particularly animal feeds for ruminants, that include hydrogenated oils, fatty acids, or waxes.
For example, U.S. Pat. No. 3,541,204 discloses hydrogenated vegetable and animal fats and waxes such as rice bran wax as coatings that survive the rumen but are disrupted in the intestinal tract.
U.S. Pat. No. 3,959,493 describes utilizing aliphatic fatty acids having at least 14 carbon atoms each. The fatty acids are applied as a coating to an individual nutrient. The fatty acids are said to be resistant to rumen degradation. The active agents are then delivered to the abomasum and/or intestine where the fatty acids are reduced in the post-ruminal environment.
U.S. Pat. No. 4,713,245 discloses a rumen-surviving granule comprising a core of bioactive material, a coating substance stable at neutral pH (as found in the rumen) but dissolved or disintegrated at pH=3 (as found in the abomasum), and at least one other coating selected from the group consisting of fatty acids having at least 14 carbon atoms and waxes, animal fat, and vegetable fat having a melting point of 40° C. or higher.
U.S. Pat. No. 5,227,166 discloses a feed supplement for ruminants consisting of a coated biologically active substance, such as an amino acid, drug, or vitamin, The coating composition comprises lecithin, at least one inorganic substance which is stable in neutrality and soluble under acidic conditions, and at least one substance selected from the group consisting of straight-chain or branched-chain saturated or unsaturated monocarboxylic acids having 14 to 22 carbon atoms, salts thereof, hardened vegetable oils, hardened animal oils, and waxes.
U.S. Pat. No. 5,807,594 describes a method of improving weight gain and feed efficiency in a ruminant by encapsulating a choline chloride composition in a rumen-protected carrier. Disclosed encapsulating or coating materials include hydrogenated oils, mono- and di-glycerides, waxes, and seed fats.
U.S. Pat. No. 6,242,013 describes a ruminally-protected high oleic material produced by roasting oilseeds at high temperatures to protect the fatty acids fed to ruminants. However, the roasting procedures require costly energy consumption.